1. Field of the Invention
The present invention relates to a method for manufacturing an Electro-Static Discharge (ESD) protection device and an ESD protection device and more specifically relates to a method for manufacturing an ESD protection device, such as a single component (ESD protection device) having only an ESD protection function and a composite component (module) having an ESD protection function and another function and an ESD protection device.
2. Description of the Related Art
ESD refers to a phenomenon such that when an electrified conductive object (human body or the like) contacts or sufficiently approaches another conductive object (electronic device or the like), intense electric discharge occurs. The ESD causes problems, such as, damaging or malfunctioning of electronic devices. In order to prevent such problems, it is necessary to prevent the application of an excessive voltage generated in electric discharge to a circuit of electronic devices. For use in such an application, an ESD protection device is provided and is also referred to as a surge absorption element or a surge absorber.
The ESD protection device is disposed, for example, between a signal line and the ground of a circuit. The ESD protection device has a structure in which a pair of electric discharge electrodes are disposed facing each other with a space provided therebetween. Therefore, the ESD protection device has high resistance in a usual use state, so that signals do not flow into the ground side. In contrast, when an excessive voltage is applied as in the case where static electricity is applied from antennas of cellular phones and the like, for example, electric discharge occurs between the electric discharge electrodes of the ESD protection device, so that the static electricity can be led to the ground side. Thus, a voltage caused by static electricity is not applied to a latter circuit relative to the ESD device, so that the circuit can be protected.
For example, an ESD protection device illustrated in an exploded perspective view of FIG. 24 and a cross sectional view of FIG. 25, a cavity portion 5 is formed in a ceramic multilayer substrate 7 in which insulating ceramic sheets 2 are to be laminated, electric discharge electrodes 6 which are conductive with external electrodes 1 are disposed facing each other in the cavity portion 5, and electric discharge gas is confined in the cavity portion 5. When a voltage causing dielectric breakdown between the electric discharge electrodes 6 is applied, electric discharge occurs between the electric discharge electrodes 6 in the cavity portion 5. The electric discharge can lead an excessive voltage to the ground, so that a latter circuit can be protected (See, for example, Japanese Unexamined Patent Application Publication No. 2001-43954).
In the ESD protection device, the firing potential is adjusted mainly by adjusting the interval of the electric discharge electrodes disposed to face each other along the main surface of the insulating layer. However, since the interval of the electric discharge electrodes is likely to vary due to device manufacturing variations, shrinkage when firing the ceramic substrate, or the like, it is difficult to adjust the interval with good accuracy. Therefore, the adjustment or the stabilization of the ESD characteristics, such as a peak voltage value, is not easily achieved. The peak voltage value refers to a peak voltage value applied to a protection circuit when a static electricity test is performed at 8 kV contact discharge based on ICE61000-4-2. When the value is lower, the static electricity inhibitory effect is more excellent.